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Threaded fasteners with level knowledge sharing

Screw threadIs a solid in cross-section of the outer or inner surface, with a uniform spiral convex shape, andThreaded fastenersRefers to the tightness of fit screwed each other between the threads, class is a combination of internal and external threads on deviations and tolerances.
For inch thread, the external thread has the following three grades: 1A, 2A, 3A. The internal thread has the following three grades: 1B, 2B, 3B, belong clearance fit, the higher the level, the tighter fit. For inch thread, 3A level deviation deviation 0,1A and 2A are the same.
1A and 1B and the level is very loose tolerance level, suitable for external and internal threads tolerances between mating; 2A and 2B level is the most common mechanical fasteners Inch tolerance level; 3A and 3B level can spin synthetic tightest fit, tight tolerances generally used for fasteners, as well as a key security design.
There tolerances, 3A grade not, under normal circumstances, 1A level tolerance than the Class 2A large fifty percent between 1A and 2A grade external thread level than 3A magnitude 75%; internal thread 2A and 2B tolerances than magnitude thirty percent, 1B level 2B magnitude than fifty percent, 3B magnitude than seventy-five percent.